1. Field of the Disclosure
This disclosure relates to a subsea wellbore system and in particular to a system and methods for attaching a riser to a subsea wellhead equipment.
2. Background of the Art
Subsea wells (also referred to as wellbores or boreholes) for the production of oil and gas are drilled into subsea formations from an offshore rig (such as a vessel). Often, the water depth exceeds 5000 feet. A riser, a hollow large diameter (e.g., 12-20 inches) flexible longitudinal tubular member, is connected between drilling equipment on the offshore rig and the wellhead equipment installed on the sea floor above the wellbore. During installation, the riser is filled with the sea water. To drill the wellbore, a drill string including a drill pipe attached to a bottomhole assembly having a drill bit at end thereof is conveyed into the wellbore through the riser. During installation of the riser, if the underwater eddy currents are strong enough, they can deflect the riser from the vertical between the offshore rig and the wellhead, which can make it difficult or unfeasible to connect the bottom end of the riser to the wellhead equipment. It is known that in the Gulf of Mexico, relatively strong sustained loop eddy currents exist, often between 2000-4000 feet depth. Such currents have at times severely disrupted oil and gas drilling activities, one of the reasons being the inability to connect the riser to the wellhead equipment. Therefore, there is a need to provide apparatus and methods for connecting a riser from an offshore rig to wellhead equipment when the riser is deflected from a vertical under the water.
The disclosure herein provides apparatus and methods for connecting a riser from an offshore rig to a wellhead equipment when the riser is deflected from the vertical.